Exceeding tape work space capacity

At the beginning of a sort using tape work data sets, DFSORT estimates the maximum sort capacity (Nmax) and issues message ICE038I. See the explanation of this message for details.

The value for Nmax printed in message ICE038I is an average value rounded down to the nearest thousand. This value assumes random input. If you have a reversed sequenced file and tape work space, sort capacity may be exceeded at a lower value because of the higher number of partly empty, end-of-string blocks.

For magnetic tape, a tape length of 2400 feet is assumed in calculating Nmax. For tapes of other lengths, the figure is not correct. When tapes with mixed density are used, the smallest density is used in the calculation.

If you specify an actual data set size, and that size is larger than the maximum capacity estimated by the program (Nmax), the program terminates before beginning to sort. If you specify an estimated data set size, or none at all, and the number of records reaches the maximum (Nmax), the program gives control to your routine at user exit E16, if you have written and included one. This routine can direct the program to take one of the following actions:

Continue sorting the entire input data set with available work space. If the estimate of the input data set size was high, enough work space may remain to complete the application.
Continue sorting with only part of the input data set; the remainder could be sorted later and the two results merged to complete the application.
Terminate the program without any further processing.

If you do not include an E16 routine, DFSORT continues to process records for as long as possible. If the work space is sufficient to contain all the records in the input data set, DFSORT completes normally; when work space is not sufficient, DFSORT issues a message and terminates.

The program generates a separate message for each of the three possible error conditions. They are:

ICE041A—N GT NMAX: Generated before sorting begins when the exact file size is greater than Nmax.
ICE046A—SORT CAPACITY EXCEEDED: Generated when the sort has used all available work space.
ICE048I—NMAX EXCEEDED: Generated when the sort has exceeded Nmax and has transferred control to a user-written E16 routine for further action.

The test for message ICE041A is made with the maximum possible calculated value, that is, DFSORT is sure it will fail. In case of doubt, the message is not issued.